准噶尔柄锈菌:新疆荒漠的雀麦锈菌——新种

本文描述了南疆雀麦Bromus gedrosianus Penz.上的锈菌一新种:准噶尔柄锈菌Puccinia junggarensis S.-X. Wei & J.-Y. Zhuang sp. nov.。模式标本采自新疆古尔班通古特沙漠克拉玛依附近,保藏在中国科学院微生物研究所真菌标本室。此菌曾被本文第二作者暂定为Puccinia burnettii Griff.。原标本经第一作者复查发现夏孢子表面纹饰为细庆而非细刺,夏孢子和冬孢子的综合特征不同于禾本科植物上迄今已知的所有柄锈菌属的种,故鉴定为新种。     

Edaphic factors and plant species distribution in a protected area in the desert of Bahrain Island

Effects of edaphic factors (salinity, pH, Na⁺, K⁺, Ca⁺⁺, CaCO₃, water holding capacity, and grain size) on the spatial distribution of plants were investigated. Soil was sampled at 22 stands. Sixteen plant species were recorded from these stands. Relation between edaphic factors and plant distribution was investigated using correlation statistical analysis. Distribution of some plants was found to be highly correlated with edaphic factor(s).     

Plant growth in relation to a rain incident in Wadi Agag,South Egypt

Plant growth in the extremely arid southern part of the Eastern Desert of Egypt is supported by the torrential moisture stored in the subsurface layers of wadi-fill deposits. The space-time stratification of the soil moisture and corresponding adaptive stratification of root systems lead to the niche separation of the species. The survivorship of all studied plants except Zilla spinosa, has a low mortality at early and middle life, but a rapid change to high mortality at a later stage. Zilla spinosa shows the high juvenile and low adult mortality which related significantly to the population density.     

Influences of root distribution and growth on predicted water uptake and interspecific competition

Summary Root distribution and growth measured in the field were incorporated into a water uptake model for the CAM succulent Agave deserti and its nurse plant Hilaria rigida, a common desert bunchgrass. Agave deserti responds to the infrequent rainfalls of the Sonoran Desert by extending its existing established roots and by producing new roots. Most of such root growth was completed within one month after soil rewetting, total root length of A. deserti increasing by 84% for a seedling and by 58% for a mediumsized plant in the summer. Root growth in the winter with its lower soil temperatures was approximately half as much as in the summer. For a 15-year period, predicted annual root growth of A. deserti varied more than 18-fold because of annual variations in rainfall amount and pattern as well as seasonal variation in soil temperature. Predicted annual water uptake varied 47-fold over the same period. The nurse plant, which is crucial for establishment of A. deserti seedlings, reduced seedling water uptake by 38% during an average rainfall year. Lowering the location of the root system of a medium-sized A. deserti by 0.24 m reduced its simulated annual water uptake by about 25%, reflecting the importance of shallow roots for this desert succulent. Lowering the root system of a medium-sized H. rigida by 0.28 m increased the simulated annual water uptake of an associated A. deserti seedling by 17%, further indicating the influence of root overlap on competition for water.     

Phytophagous insects enhance nitrogen flux in a desert creosotebush community

Summary We tested the hypothesis that herbivorous insects on desert shrubs contribute to short-term nitrogen cycling, and increase rates of nitrogen flux from nutrient rich plants. Creosotebush (Larrea tridentata) shrubs were treated with different combinations of fertilizer and water augmentations, resulting in different levels of foliage production and foliar nitrogen contents. Foliage arthropod populations, and nitrogen in canopy dry throughfall, wet throughfall and stemflow were measured to assess nitrogen flux rates relative to arthropod abundances on manipulated and unmanipulated shrubs over a one-month period during peak productivity. Numbers and biomass of foliage arthropods were significantly higher on fertilized shrubs. Sap-sucking phytophagous insects accounted for the greatest numbers of foliage arthropods, but leaf-chewing phytophagous insects represented the greatest biomass of foliage arthropods. Measured amounts of bulk frass (from leaf-chewing insects) were not significantly different among the various treatments. Amounts of nitrogen from dry and wet throughfall and stemflow were significantly greater under fertilized shrubs due to fine frass input from sap-sucking insects. Increased numbers and biomass of phytophagous insects on fertilized shrubs increased canopy to soil nitrogen flux due to increased levels of herbivory and excrement. Nitrogen excreted by foliage arthropods accounted for about 20% of the total one month canopy to soil nitrogen flux, while leaf litter accounted for about 80%.     

塔里木沙拐枣果实刺毛对果实扩散及萌发的影响

塔里木沙拐枣（Calligonum roborowskii A.Los.）是仅分布于我国西北地区荒漠环境的特有种,其果实为不开裂而周围有椭圆形刺毛的瘦果,以果实为单元进行扩散和萌发。本文采用野外观察与室内控制实验相结合的方法,对塔里木沙拐枣刺毛在果实扩散、吸水、脱水及萌发中的作用进行研究。结果显示：不同贮藏时间的果实颜色、大小、重量及刺毛长度存在显著差异。完整果实在水面漂浮时间及水媒扩散能力比去除刺毛的果实更强。完整果实在1 m/s和4 m/s风速下的扩散距离比无刺毛果实的扩散距离长。10 mmol/L赤霉素（AG₃）及不同干藏时间处理的完整果实与无刺毛果实在20℃/30℃光照和黑暗条件下的萌发率间存在显著差异,其中无刺毛果实的萌发率要高于完整果实的萌发率。室外盆栽实验显示,无刺毛果实的萌发率比完整果实高,说明果实刺毛对果实萌发有抑制作用。研究结果表明果实刺毛对塔里木沙拐枣在塔克拉玛干沙漠边缘荒漠环境中的扩散、萌发及种群更新具有重要的辅助作用。     

北美CHIHUAHUAN荒漠啮齿动物群落动态Ⅱ．季节性和周期性

本文利用时间序列分析方法和季节性指标,讨论了北美Ｃｈｉｈｕａｈｕａｎ荒漠由４科１０属１７种啮齿动物组成的群落的物种数、单位面积个体数与生物量、物种多样性的Ｓｈａｎｎｏｎ与Ｓｉｍｐｓｏｎ指数和均匀性等６个变量的季节变动、季节性和周期性。结果表明：（１）每个季节都有变量达到最大值,但除个体数和均匀性外,其余４个变量均在冬季达到最小值;（２）物种数与生物量及两个物种多样性指数之间,以及两个物种多样性指数相互之间有类似的季节变动规律;（３）除个体数外,群落数量动态的其他变量与８个物种种群的密度存在着显著的负相关关系;（４）物种数有最明显的季节性,季节性指标ＳＩ＝０．６２８;（５）物种数、个体数和生物量在９２个月的研究期中未显示出任何周期性。最后总结了该啮齿动物群落动态的时间模式,提出组成物种种群的扩散和休眠行为是形成这些模式的主要原因。     

Plant species diversity and ecological districts of the Sinai desert

Summary Lists of vascular plant species for each of the 12 ecological districts of Sinai were prepared. In all 78,000 observations on altogether 812 species were analyzed. The number of districts where each species occurred was also counted. Linear regressions were calculated for the log-transformed values of species/area, species/altitude and multiple regression of species on both area and altitude.The regression of species on area for the 12 ecological districts of Sinai gave the equation: log S = 1.0309+0.3 log A The value of z=0.3 is higher than 0.222—the measured overall value for the continents and higher than the values for the Sahara, California mainland, the British Isles, and the Netherlands. However, it is lower than the values for the Galápagos Archipelago and the California Islands.The number of species supported in districts characterized by fissured limestone, gravel plains, chalk, marl, sandstones, sands or fissured magmatic and metamorphic rocks is close to the regression of species on area, whereas large outcrops of smooth-faced rocks are relatively richer in total number of species as well as in stenotople species.It is suggested that the high gamma diversity of Sinai as compared with other parts of the world is primarily due to its environmental heterogeneity. Sinai being a meeting place of three phytogeographical regions and to past climatic changes. The effect of smooth-faced rock outcrops as conducive to providing refugia must also be taken into account.This work is based on a comprehensive study of the vegetation of Sinai directed by Prof. G. Orshan, with the collaboration of Dr. A. Shmida, the present author and the late Prof. N.H. Tadmor and Dr. G. Halevy.     

Nutrient mobilization and processing in Sonoran desert riparian soils following artificial re-wetting

Research in river-floodplain systems has emphasized the importance of nutrient delivery by floodwaters, but the mechanisms by which floods make nutrients available are rarely evaluated. Using a laboratory re-wetting experiment, we evaluated the alternative hypotheses that increased nutrient concentrations in riparian groundwater during flash floods are due to (H1) elevated nutrient concentrations in surface floodwaters entering the riparian zone or (H2) re-mobilization of nutrients from riparian soils. We sampled soils from the riparian zone of a 400m reach of Sycamore Creek, AZ. Two sub-samples from each soil were re-wetted with a solution that mimicked the chemistry of floodwaters, with one sub-sample simultaneously treated with a biocide. We also measured structural characteristics of soils (texture, organic matter, moisture, and extractable nutrients) to investigate relationships between these characteristics and response to re-wetting. Riparian soils exhibited considerable variation in physical and chemical structure. Soil organic matter, moisture, and texture co-varied among samples. Re-wetting increased concentrations of nitrate and ammonium, and decreased SRP, relative to initial concentrations. Live soils were significantly lower in NO3-and SRP than biocide-treated samples. Extractable DIN pools were the best predictors of mobilization, and soil organic matter was strongly correlated with nitrate losses, probably via its relationship with microbial uptake. Nutrient mobilization and processing also varied considerably with depth, lateral position, and among plots. We estimate that 70–80% of N in riparian groundwater during flash floods is re-mobilized from riparian soils, but are unable to reject the hypothesis that flood inputs may be important sources of nutrients to riparian soils over longer time scales.